Conventionally, for an electric power source of a piece of electric equipment attached to an overhead power line, a battery is used. Nevertheless, due to a lifetime of the buttery, in a two- or three-year cycle, an exchange of the battery is carried out in a hot line work manner or a power cut manner.
On the other hand, there is a case where a solar battery is used for an electric power source of a piece of electric equipment attached to an overhead power line. Nevertheless, since the solar battery must be large-scale in order to secure a sufficient generation capacity, it is difficult to attach the large-scale solar battery to an overhead power line. Also, a battery must be used together with the solar battery in order to ensure an operation of a piece of electric equipment for the night. As a result, there is a problem that not only weight of the electric power source is increased, but also an exchange of the battery is needed.
For this reason, at present, the electric power source system concerned, which involves a frequency of maintenance to an overhead power line causing a high possible electric shock as a high voltage power line, does not widely prevails.
In this circumstance, attempts have been made to develop an apparatus which can obtain an electric power by attaching it to an overhead power line without any battery, and which can secure an electric power even if any current does not flow through the overhead power line.
For example, in a conventional night indicator device of an overhead power transmission line, one terminal of a neon discharge tube is adhered to the power transmission line, and the other terminal of the neon discharge tube is coated with an insulating material, and is wound around the power transmission line at suitable intervals. It is disclosed that the neon discharge tube is lighted due to electrostatic induction caused between the coated line and the power transmission line. Also, it is disclosed as conventional arts that an overhead power transmission line is covered with a metal pipe, ends of which are coaxially held with dielectric materials, and that a damper line made of conductor is suspended from an overhead power transmission line through an insulator (for example, see: Patent Document 1).
Also, as a conventional electrostatic induction type electric power supply apparatus, is disclosed an apparatus including an insulator spirally wound around a power line conductor in an electrical substation, an electrode spirally wound over the insulator, and a rectifying circuit in which an input lead drawn from the electrode and an input lead drawn from the power line conductor are used as a primary side input, and in which a secondary side is connected to a sensor (for example, see: Patent Document 2).
Also, as a conventional electric power supply apparatus for a measurement device of a power transmission/distribution system, is disclosed an apparatus including a protecting circuit for converting a voltage obtained from a spatial electrode into a suitable voltage to thereby controlling an excess voltage, a rectifying circuit for converting an voltage from the protecting circuit from an alternating current into a direct current, a storage battery for storing electricity output from the rectifying circuit, a voltage detector for detecting a voltage of the storage battery, and a voltage generator for intermittently outputting a necessary voltage to a load of a measurement device based on a detected voltage (for example, see: Patent Document 3).    Patent Document 1: JUM-S39-29852 A    Patent Document 2: JP-H10-262349 A    Patent Document 3: JP-2003-284252 A